Hybrid electric vehicles currently employ electric motors in conjunction with an internal combustion engine (usually gasoline or diesel) to improve gas mileage by permitting the engine to operate more efficiently. Typically, the motor is used either during the entire operation of the vehicle, alone, or in conjunction with the combustion engine during times that would be most inefficient for the engine, such as upon starting the vehicle and during much of the acceleration. The combustion engine is used either to power the vehicle or recharge the battery of the motor when the motor is not in use. Therefore, the engine is generally used in optimum or more efficiently favorable conditions, thus optimizing engine performance and saving fuel.
Some vehicles use a turbocharger to use waste heat from the vehicle exhaust to provide extra power to the vehicle. In some cases, a turbine is positioned in the exhaust path to turn the waste heat into mechanical energy. The turbine is then generally coupled to a compressor that is used to compress the air into the engine. The compressed air permits additional fuel to be injected into the engine and combusted to provide additional power for the same component space.
The cost of a hybrid vehicle is generally greater than that of a comparative internal combustion engine vehicle. The cost is at least partially deferred by the savings in gasoline. However, the gas efficiency of a hybrid vehicle may not be sufficiently high to encourage customers to choose a hybrid without other incentives. In certain cases, some mid-sized hybrid vehicles may get equal or less gas mileage compared to select compact internal combustion engine cars.